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      <title>如何通过UDP协议实现数据传输的可靠性？ - 交互式测验</title>
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            <div class="quiz-header">
              <h1>如何通过UDP协议实现数据传输的可靠性？ - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "根据文档，UDP协议本身不提供可靠性保证。那么，为了确保数据可靠传输，通常需要在哪个层面实现额外的机制？",
    "options": [
      "网络层 (Network Layer)",
      "应用层 (Application Layer)",
      "物理层 (Physical Layer)",
      "传输层 (Transport Layer)"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档开篇就明确指出，UDP（用户数据报协议）本身不提供内建的可靠性保证，通常需要在应用层实现额外的机制（如确认、重传等）来保证数据的可靠性。传输层是UDP协议所在的层，但文档讨论的增强机制是在其之上的应用层实现的。",
    "source": "文档开篇引言部分",
    "hint": "文档提到“通常需要在...实现额外的机制来保证数据的可靠性”。"
  },
  {
    "question": "在基于UDP的可靠传输方案中，引入“序列号 (Sequence Numbers)”机制的主要目的是什么？",
    "options": [
      "防止发送方发送过多的数据包，超出接收方的处理能力。",
      "为每个数据包提供唯一的身份标识，主要用于数据加密。",
      "确保数据包能够按序到达并帮助检测丢失的数据包。",
      "检测数据包在传输过程中是否因比特错误而损坏。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档指出，为每个发送的数据包分配唯一的序列号，是为了让接收方能够根据序列号对数据包进行排序，确保数据按正确顺序交给应用层。同时，通过检查序列号的连续性，接收方可以判断是否有数据包丢失。",
    "source": "文档中「3. 序列号（Sequence Numbers）」部分",
    "hint": "考虑一下当数据包乱序或丢失时，接收方需要什么信息来重组它们或发现缺失。"
  },
  {
    "question": "关于UDP的“校验和 (Checksum)”机制，以下哪个描述是正确的？",
    "options": [
      "校验和机制可以自动修复在传输中损坏的数据包。",
      "UDP协议本身提供了校验和功能来检测数据损坏，如果校验失败，接收方会丢弃数据包，需要应用层来处理后续问题。",
      "校验和是完全在应用层实现的，UDP协议本身不参与任何校验过程。",
      "校验和机制保证了数据包一定能够成功送达接收方。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档明确说明，UDP协议本身支持校验和，用于检测数据包在传输过程中是否发生了损坏。但它的作用仅限于检测。当接收方发现校验和不匹配时，会丢弃该数据包。因此，数据包的丢失问题需要由应用层通过其他机制（如重传）来解决。",
    "source": "文档中「5. 校验和（Checksum）」部分",
    "hint": "文档提到“UDP协议本身支持校验和”，但“如果校验和不匹配，接收方会丢弃数据包，应用层需要处理数据包的丢失问题”。"
  },
  {
    "question": "在应用层实现的“重传机制 (Retransmission)”通常依赖于哪两个配套机制来判断是否需要重传？",
    "options": [
      "流量控制 (Flow Control) 和序列号 (Sequence Numbers)",
      "自定义协议层 (Custom Protocol Layer) 和校验和 (Checksum)",
      "数据包确认 (Acknowledgment) 和超时 (Timeout)",
      "序列号 (Sequence Numbers) 和数据完整性检查 (Data Integrity Checks)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "根据文档，“重传机制”的工作原理是：发送方发送数据包后启动一个计时器（超时机制），如果在超时时间内没有收到来自接收方的“确认消息（ACK）”，发送方就会重新发送该数据包。因此，重传是建立在确认和超时机制之上的。",
    "source": "文档中「1. 数据包确认（Acknowledgment）」和「2. 重传机制（Retransmission）」部分",
    "hint": "发送方如何知道一个数据包已经成功被接收，或者它可能已经在网络中丢失了？"
  },
  {
    "question": "文档中提到的“流量控制 (Flow Control)”机制，其核心目的是解决什么问题？",
    "options": [
      "确保数据包按照正确的顺序被处理。",
      "检测并纠正数据在传输过程中的错误。",
      "防止因发送方发送速度过快，导致接收方处理不过来而丢弃数据包。",
      "控制网络拥堵，避免整个网络链路瘫痪。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档描述流量控制的目的是“避免发送方发送过多的数据包超出接收方的处理能力”。其工作原理是通过一种机制让发送方了解接收方的缓存或处理能力，从而调整发送速率，“防止数据包的溢出和丢失”。",
    "source": "文档中「4. 流量控制（Flow Control）」部分",
    "hint": "这个机制主要关注的是接收方的“处理能力”，防止其被数据淹没。"
  },
  {
    "question": "根据文档，当需要在UDP之上实现一套完整的可靠性保障时，可以采用“自定义协议层 (Custom Protocol Layer)”的方式。这种方式的最大特点是什么？",
    "options": [
      "它是一种由UDP协议内建的、可以自动开启的可靠性模式。",
      "它完全取代了UDP协议，直接在IP层上工作以提高效率。",
      "它允许应用程序根据自身具体需求，灵活地组合和实现确认、重传、排序等多种可靠性功能。",
      "它主要用于数据的加密和安全认证，而非传输可靠性。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中提到，“自定义协议层”是在UDP之上构建的，应用程序可以设计和实现自己的协议层来处理数据包的确认、重传、排序等功能。这使得应用层可以“根据具体需求自定义可靠性保障措施”，体现了其高度的灵活性和可定制性。",
    "source": "文档中「7. 自定义协议层（Custom Protocol Layer）」部分",
    "hint": "文档中描述这种方法使得应用层可以“根据具体需求自定义可靠性保障措施”。"
  },
  {
    "question": "文档提到了两种用于保证数据准确性的机制：“校验和 (Checksum)”和“数据完整性检查 (Data Integrity Checks)”。它们之间的一个关键区别是什么？",
    "options": [
      "“校验和”由UDP原生支持，“数据完整性检查”则是在应用层实现，通常使用更强的算法（如哈希函数）。",
      "“校验和”只能检测错误，“数据完整性检查”可以自动修复错误。",
      "两者没有区别，只是不同场景下的同义词。",
      "“校验和”用于检查包头，“数据完整性检查”用于检查包体。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "文档在“校验和”部分指出这是UDP协议本身支持的机制。而在“数据完整性检查”部分，则描述为在应用层实现的机制，例如通过哈希函数计算校验和。这表明应用层的完整性检查可以提供比UDP自带校验和更强的保证，是应用层面的额外增强。",
    "source": "文档中「5. 校验和（Checksum）」和「8. 数据完整性检查（Data Integrity Checks）」部分",
    "hint": "请注意这两个机制在文档中被分别列出，并思考它们是在协议的哪一层实现的。"
  }
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                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  